README.md

Contact information and license

PropEr (PROPerty-based testing tool for ERlang) is a QuickCheck-inspired
open-source property-based testing tool for Erlang, developed by Manolis
Papadakis, Eirini Arvaniti and Kostis Sagonas. The base PropEr system was
written mainly by Manolis Papadakis, and the stateful code testing subsystem by
Eirini Arvaniti.

This program is distributed under the GPL,
version 3 or later. Please see the COPYING file for details.

Introduction

Traditional testing methodologies essentially involve software testers writing a
series of test inputs for their programs, along with their corresponding
expected outputs, then running the program with these inputs and observing
whether it behaves as expected. This method of testing, while simple and easy to
automate, suffers from a few problems, such as:

Writing test cases by hand is tedious and time consuming.

It is hard to know whether the test suite covers all aspects of the software
under test.

Property-based testing is a novel approach to software testing, where the tester
needs only specify the generic structure of valid inputs for the program under
test, plus certain properties (regarding the program's behaviour and the
input-output relation) which are expected to hold for every valid input.
A property-based testing tool, when supplied with this information, should randomly
produce progressively more complex valid inputs, then apply those inputs to the
program while monitoring its execution, to ensure that it behaves according to
its specification, as outlined in the supplied properties.

Here are a few examples of simple properties a user may wish to test, expressed
in natural language:

The program should accept any character string and convert all lowercase
letters inside the string to uppercase.

The program should accept any list of integers. If the input list is at
least 4 elements long, the program should return the 4th largest integer in
the list, else it should throw an exception.

PropEr is such a property-based testing tool, designed to test programs written
in the Erlang programming language. Its focus is on testing the behaviour of
pure functions. On top of that, it is equipped with two library modules that can
be used for testing stateful code. The input domain of functions is specified
through the use of a type system, modeled closely after the type system of the
language itself. Properties are written using Erlang expressions, with the help
of a few predefined macros.

PropEr is also tightly integrated with Erlang's type language:

Types expressed in the Erlang type language can be used instead of
generators written in PropEr's own type system as input data specifications.

Generators for ADTs can be constructed automatically using the ADTs' API
functions.

PropEr can test functions automatically, based solely on information
provided in their specs.

Quickstart guide

Obtain a copy of PropEr's sources. You can either get a tagged version of
the tool (look under Tags on github) or you can clone the current code
base:

git clone git://github.com/manopapad/proper.git

Compile PropEr: Run make if you just want to build PropEr, optionally
followed by a make tests to run its unit tests and a make dialyzer call
to also run dialyzer on PropEr's code base; the latter requires having a
dialyzer PLT. To do the above but also build PropEr's documentation issue
a make all call; in that case, you are going to need the syntax_tools
application and a recent version of EDoc).
Optionally, sfmt-erlang can be selected as an alternative random number
generator using ./configure --use-sfmt before running make.

Add PropEr's base directory to your Erlang library path, using one of the
following methods:

ERL_LIBS environment variable: Add the following line to your shell
startup file (~/.bashrc in the case of the Bash shell):

export ERL_LIBS=/full/path/to/proper

Erlang resource file: Add the following line to your ~/.erlang file:

code:load_abs("/full/path/to/proper").

If using the sfmt RNG be sure to add /full/path/to/proper/deps/sfmt too.

Add the following include line to all source files that contain properties:

-include_lib("proper/include/proper.hrl").

Compile those source files, preferably with debug_info enabled.

For each property, run:

proper:quickcheck(your_module:some_property()).

See also the section common problems below if you want to run
PropEr from EUnit.

Where to go from here

To get started on using PropEr, see the tutorials and testing tips provided on
PropEr's home page. On the same site you can
find a copy of PropEr's API documentation (you can also build this from source
if you prefer, by running make doc), as well as links to more resources on
property-based testing.

Common problems

Using PropEr in conjunction with EUnit

The main issue is that both systems define a ?LET macro. To avoid a potential
clash, simply include PropEr's header file before EUnit's. That way, any
instance of ?LET will count as a PropEr ?LET.

Another issue is that EUnit captures standard output,
so normally PropEr output is not visible when proper:quickcheck() is
invoked from EUnit. You can work around this by passing the option
{to_file, user} to proper:quickcheck/2. For example:

This will make PropEr properties visible also when invoked from EUnit.

Incompatibilities with QuviQ's QuickCheck

PropEr's notation and output format has been kept quite similar to that of
QuviQ's QuickCheck in order to ease the reuse of existing testing code written
for that tool. However, incompatibilities are to be expected, since we never
run or owned a copy of QuviQ's QuickCheck and the two programs probably bear
little resemblance under the hood. Here we provide a nonexhaustive list of
known incompatibilities:

?SUCHTHATMAYBE behaves differently in PropEr.

proper_gen:pick/1 differs from eqc_gen:pick/1 in return value format.

PropEr handles size differently from QuickCheck.

proper:module/2 accepts options in the second argument instead of the
first; this is for consistency with other module/2 functions in Erlang/OTP.